End stage renal disease (ESRD), the permanent loss of kidney function, is an increasing threat to healthcare across all societies worldwide. Currently, the preferred treatment for ESRD is kidney transplantation, but this option is limited by the shortage of donor organs and complications due to rejection and immunosuppression. Dialysis, the second treatment option for ESRD, is cost intensive and associated with morbidity as well as poor quality of life.
Regenerative medicine is working towards developing methods to overcome these limitations through, for example, in vitro kidney organogenesis. The kidney develops from two main cell types, the ureteric bud (UB) cells and the metanephric mesenchymal (MM) cells (FIG. 1). In the embryo, these two cell types are arranged in a specific way. The UB cells take the shape of a tube as an outgrowth of the Wolfian duct (WD), while the MM cells are aggregated in a sphere. Renal development starts when the UB cells are attracted by growth factors released from the MM cells and grow into the MM sphere to form the branched tubular structure of the kidney collecting system. In a reciprocal manner, the UB cells release factors to induce MM cells to differentiate and develop into the remaining structures of the kidney.
A population of cells present in the MM, the stromal cells (SC), also has important functions in the developing kidney. Studies have demonstrated that a signaling loop exists between UB and SC. SC secrete signals to control RET expression and branching morphogenesis in UB cells, and adequate RET expression regulates normal SC patterning (Cullen-McEwen, Nephron Exp Nephrol, 2005). SC have also been suggested to promote the differentiation of MM (Das, Nature Cell Biology, 2013) and to contribute to vascular development (Sequeira-Lopez, Am J Physiol, 2014).
It has been demonstrated that an early stage embryonic kidney can be implanted in a mouse where it can develop into a mature and vascularized adult kidney (Rogers, Am J Physiol, 2001). It has further been shown that UB and MM cells have strong self-organizational potential and are able to form renal structures from single cell suspension in vitro (Unbekandt, Kid Intl, 2010), where embryonic kidneys were isolated at e11.5 and a single cell suspension was produced from UB and MM cells. The cells were re-aggregated by centrifugation and cultured in vitro as shown in FIG. 2, (reproduced from Unbekandt, Kid Intl, 2010). After 5-7 days, these aggregates contained simple renal structures (see also Ganeva, Organogenesis, 2011). Generation of tubular structures with a micropatterned gel from two dispersed UB-derived mouse cell lines has also been demonstrated (Hauser, J. Tissue Eng. Regen. Med., 2014; the disclosure of which is hereby incorporated by reference in its entirety).
These studies demonstrated that kidney progenitor cells (UB, MM, and SC) have a high self-organizing potential and are able to generate kidney structures. These experiments, however, also showed that the self-organization potential of the renal progenitor cells is limited. The kidney structures generated were disconnected and did not form the type of integrated, branched collecting duct structure necessary to excrete the filtered waste products (FIG. 3A-3B). Since a major function of the kidney is the filtration of blood and the draining of waste product through a centralized collecting duct system, this conventional re-aggregation method is not sufficient to develop into a functional organ.
There is therefore an urgent need for an improved system for kidney organogenesis to generate better functioning kidneys for treatment of ESRD. The present invention addresses this need.